[A-CG31] Nutrient footprint of primary production in the coastal and marginal seas of East and Southeast Asia

[ACG31-06] A significant contribution of open ocean to nutrient and phytoplankton inventory in the Seto Inland Sea

*LENG QIAN¹, Xinyu Guo¹, Akihiko Morimoto¹ (1.Center for Marine Environmental Studies, Ehime University)

Keywords:Nitrogen inventory, Oceanic nutrient, Semi-enclosed sea

The semi-enclosed coastal seas serve as a transition region from land to the open ocean and are affected by both, but the role of the open ocean remains unclear. The Seto Inland Sea (SIS), which is connected to the Pacific Ocean, is a typical one of semi-enclosed seas. We developed a three-dimensional coupled physical-biogeochemical model, embedded with a nutrient source tracking technique, to quantitatively assess the material inventory of SIS originating from the open ocean. Our model shows that the open ocean contributes 73% and 60% of the annual mean dissolved inorganic nitrogen (DIN) and phytoplankton (PHY) inventories across the SIS, implying a large proportion of open ocean origin. The oceanic contribution to the total DIN and PHY inventory decreased from the south part of SIS to the interior, showing lower values in the nearshore areas. The open ocean imported 797 mol/s DIN to the SIS each year, among which 25% was consumed by biogeochemical processes in the SIS while the other returned to the open ocean again. Our results indicated the significant effect of the open ocean in typical semi-enclosed seas, suggesting the need to consider the impact of open ocean nutrient input associated with climate change when performing nutrient management.